1. Field of the Invention:
The present invention relates to a pinless folding machine applicable to a rotary folding machine.
2. Description of the Prior Art:
At first, description will be made on one example of the known pinless folding machine in the prior art with reference to FIGS. 5 and 6. As shown in FIG. 5, in a pinless folding machine in the prior art, either a web (a web of paper) a twice-folded by a triangular plate 1 or a web b in an unfolded state passes through a pair of first nipping rollers 2 and a pair of second nipping rollers 3 which are rotating at the same peripheral speed as the web speed, and then it is cut by a cutting device consisting of a cutter drum 4 and a cutter receiver drum 5. This cut paper sheet (hereinafter called simply "sheet") is accelerated by a pair of speedup conveyor belts 6 and 6' guided by a pair of guide rollers 15 and 15', so that the interval between the preceding sheet and the succeeding web is broadened. Owing to existence of this broadened interval, the head end of the succeeding sheet can be clamped by means of a folding drum 7 and a claw 8 shown in FIG. 6 without being interfering with the tail end of the preceding sheet. The clamped sheet has its central portion of the cut length pushed into the gap between a clamping plate and its seat forming a clamping device 11 on a clamping drum 10 by means of a folding blade 9 of the folding drum 7 that is accelerated to have the same peripheral speed as the speed-up conveyor belts 6 and 6' to be twice-folded, and thereafter it is carried out to the outside of the folding machine by means of conveyor belts 12, a sheet discharge impeller 13 and a sheet discharge conveyor 14. While the head end of the web is paid off from the above-mentioned cutting device and enters between the pair of speed-up conveyor belts 6 and 6' before its tail end is cut, the head portion of the web is slipping with respect to the pair of speed-up conveyor belts 6 and 6' until the tail end of the web is cut. Subsequently, when the sheet has been cut and released from the web, the sheet is quickly accelerated by the speed-up conveyor belts 6 and 6' and is conveyed to the folding drum 7. In FIG. 6, the claw 8 serves to clamp the sheet between it and a claw seat 8', but unless a gap interval S broader than a back portion 8a is present, the back portion 8a would strike against the tail end of the preceding sheet. It is to be noted the sheet clamping surfaces of the claw 8 and the claw seat 8' conform to the circumferential surface of the folding drum 7.
The above-described pinless folding machine in the prior art inherently has the following disadvantages:
(1) Since the sheet is quickly accelerated (by 15-40%) from the web speed after the web (web of paper) has been cut, faults such as end-folding, especially end-folding of the opposite edge portions projecting from the speed-up conveyor belts, a poor folding precision of sheets, or the like are liable to occur.
(2) Due to the fact that while the sheet is pinched between the aforementioned belts and is being conveyed and slipping, it is quickly paid off (accelerated) after cutting of its tail end, the head end positions of the sheets would fluctuate, and so, the head end portions would not enter uniformly into a predetermined clamping zone of the claw. Accordingly, a folding precision is degraded.
(3) Since the web is made to slip with respect to the speed-up conveyor belts (before cutting at the tail end), there occurs faults such that patterns printed on the sheet are scratched by the belts.
(4) Since the web is cut while it is held between the speed-up conveyor belts and being made to slip with respect to the belts and after cutting it is conveyed as being pinched between the belts, severe adjustment of the belts is necessary, hence a lot of labor is spent for that purpose, and it is necessary to become skilled in the adjustment.
(5) As the sheet is cut out while the web is being made to slip between and with respect to the speedup conveyor belts, static electricity is liable to be generated, consequently sometimes the fluctuations of the head end position of the sheet as described in numbered paragraph (2) above may arise, and further in the event that a resistance force caused by static electricity is uneven in the widthwise direction of the web (in the axial direction of the folding drum), the sheet would be twisted and would be folded obliquely with respect to the edges of the sheet. In addition, it becomes difficult to correct the attitude of the sheet folded on the sheet discharge conveyor.
(6) Though the sheet enters into the folding drum as guided by the speed-up conveyor belts, when the sheets have clogged the passageway between the belts, it takes a lot of time for removing the clogged sheets, and so, an availability factor of the folding machine is lowered.
(7) Since the head end of the sheet is clamped by means of a plurality of claws on the folding drum that is rotating at the increased speed, end folding of the opposite edge portions of the sheet projecting from the claws at the opposite ends, and breaking and end folding of the sheet caused by inflation of the sheet end portions between the claws, are liable to occur. In addition, as the central portion of the cut sheet is folded under the accelerated condition, a folding precision is also liable to degraded.
The above-mentioned disadvantages (1) to (7) would be more and more deteriorated as the folding machine is speeded up.